The present invention relates to inflators for vehicle airbags and, more particularly, to a linear inflator which discharges inflation gas along the length of the inflator for use in side impact or head curtain airbag systems.
In certain applications, such as a side-curtain for rollover protection, it is desirable to have an airbag that remains inflated for up to 5-10 seconds. In addition, the same airbag must protect the occupant during the “first impact” stage of an accident, which is typically 0-100 msec. Prior art inventions have solved this problem by using a stored gas inflator with a sealed air bag. In this case, the gas bottle produces relatively cool gas in a short period of time-generating enough pressure to protect the occupant from 0-100 msec. Since the bag is sealed and the gas is cool, the gas pressure in the bag at 5 seconds after impact typically drops to about 50% of the pressure generated during the first impact. The pressure drops primarily because the gas temperature decreases due to heat transfer.
Due to certain disadvantages of a stored gas inflator (size, cost, weight, and reliability for example), it is desirable to use a pyrotechnic inflator for airbag inflation. However, a typical pyrotechnic inflator produces gas that is relatively very hot thereby introducing other engineering concerns. In this case, the first impact pressure is in the desired range, but the gas pressure drops quickly due to heat transfer and the bag pressure at 5 seconds is too low to provide any protection. The pyrotechnic linear inflators described in co-owned and co-pending U.S. application Ser. Nos. 09/846,004, 10/662,771, 60/520,956, and 60/536,134, herein incorporated by reference, provide a significantly cooler gas than typical pyrotechnic inflators and can meet the same requirements as a stored gas inflator in a sealed bag.
Because it is expensive to produce an airbag that is completely sealed, it is desirable to have an inflator that will produce gas for longer than 100 msec., more preferably for longer than 1 second. U.S. application Ser. Nos. 09/846,004, 10/662,771, 60/520,956, and 60/536,134 also describe linear pyrotechnic inflators that will burn for an extended period of time. This is useful, but because some of the propellant burns at a very low pressure, the gaseous effluents may in some circumstances not meet required specifications.